Manufacturing method of ultra-large copper grains without heat treatment

ABSTRACT

A film of single crystal copper is manufactured by means of electrodeposition without heat treatment. The grains of the single crystal copper have an average size of at least 10 μm. The electrolytic solution used in the method contains chloride ions, a wetting agent, sulfuric acid, CuSO 4 .5H 2 O and alkanesulfonate sulfide. The ultra-large copper grains of the present invention contain very few impurities and thus possess low resistance, high conductivity, shining appearance and anti-fingerprint property.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a manufacturing method of ultra-largecopper grains, an electrolytic solution employed therein, and a copperfilm composed of the copper grains. More particularly, this methodcomprises an electrodeposition process without heat treatment. Thecopper grains have an average size of at least 10 μm.

2. Prior Art

In general, the copper film is made by depositing copper on a conductivesubstrate through the electroplating or sputtering process. Such copperfilm is composed of fine copper grains with an average size less than100 nm. The copper films with larger grain sizes possess betterconductivity or reliability and can be applied to different fields.Traditionally, the large copper grains are manufactured through the heattreatment or calendaring process.

The known technologies relating heat treatment include:

U.S. Pat. No. 6,126,761 (CN1056613C) discloses a process of controllinggrain growth in metal films, which comprises: (a) depositing the metalfilm onto the substrate to form a film having a fine-grainedmicrostructure, and (b) heating the metal film in a temperature range of70-100° C. for at least five minutes, wherein the fine-grainedmicrostructure is converted into a stable large-grained microstructureof an average crystallite size greater than 1 micron.

US20150064496 (TWI507569, CN104419983A) discloses a method formanufacturing a single crystal copper, in which an electroplating isperformed to grow a nano-twinned crystal copper pillar on a surface ofthe cathode. The nano-twinned crystal copper pillar comprises aplurality of nano-twinned crystal copper grains. The cathode with thenano-twinned crystal copper pillar is then annealed at 350-600° C. for0.5-3 hours to obtain a single crystal copper. The single crystal copperhas a [100] orientation and a volume of 0.1 μm³-4.0×10⁶ μm³.

US20160168746A1 (TWI545231) discloses a copper film with large grains.The grains are grown along a crystal axis direction [100], and anaverage size of the grains is 150-700 μm. A manufacturing method of thecopper clad laminate comprises: growing copper grains on one surface ofa laminate by electroplating to obtain a [111]-oriented nano-twinnedcopper film; and annealing the [111]-oriented nano-twinned copper filmunder a temperature of 200-500° C. to obtain a copper film with largegrains.

To perform the heat treatment, heating equipment is necessary and timeand temperature have to be controlled. The processes includingelectroplating and heat treatment are complex and increase the cost. Inaddition, the heat treatment may cause diffusion of impurity in thecopper and thus reduce conductivity.

SUMMARY OF THE INVENTION

The manufacturing method of ultra-large copper grains according to thepresent invention is performed without heat treatment.

This method comprises steps of: A. providing an electrodepositequipment; and B. performing an electrodeposition process using theelectrodeposit equipment with a current density of 1-80 A/dm².

In step A, the electrodeposit equipment primarily comprises an anode, acathode, an electrolytic solution, a power unit, a temperaturecontroller, and a mixer. The anode and the cathode respectively connectto the power unit and are immersed in the electrolytic solution. Thetemperature controller contacts the electrolytic solution to control theelectrolytic solution at 25-55° C. The mixer is used to fast agitate theelectrolytic solution. The electrolytic solution is obtained by mixingand dissolving chemical components such as chloride ions, wetting agent,sulfuric acid, copper sulfate and sulfur-containing compound having theformula (1) together in deionized water,

R₁—S—C_(n)H_(2n)—R₂   (1)

wherein R₁═—H, —S—C_(n)H_(2n)—R₂ or —C_(n)H_(2n)—R₂;

-   -   R₂═SO₃ ⁻, PO₄ ⁻ or COO⁻;    -   n=2-10.

In step B, ultra-large single crystal copper grains having an averagesize of at least 10 μm are deposited on a surface of the cathode to forma layer of copper grains. The sulfur-containing compound preferably isalkanesulfonate sulfide (R—S—C_(n)H_(2n)—SO₃ ⁻).

Examples of the sulfur-containing compound include3-Mercaptopropanesulfonate (MPS), Bis-(3-sulfopropyl)-disulfide (SPS),3-(2-Benzthiazolylthio)-1-propanesulfonate (ZPS),3-(N,N-Dimethyl-thiocarbamoyl)-thiopropanesulfonate (DPS),(O-Ethyldithiocarbonato) —S-(3-sulfopropyl)-ester (OPX),3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and3,3-Thiobis(1-propanesulfonate (TBPS).

A copper film is manufactured by the method aforementioned. The copperfilm comprises a plurality of the ultra-large single crystal coppergrains having an average size of at least 10 μm.

By performing an electrodeposition process in the electrolytic solution,the ultra-large single crystal copper grains having an average size ofat least 10 μm are deposited on the cathode.

The sulfur-containing compound preferably is alkanesulfonate sulfide(R—S—C_(n)H_(2n)—SO₃ ⁻).

The present invention further comprises a connecting structure ofelectric elements comprising the ultra-large copper grains produced bythe aforementioned method. The connecting structure of electric elementscomprises:

a copper pad comprising the ultra-large copper grains having an averagesize of at least 10 μm;

a solder unit soldered on a surface of the copper pad; and

an intermetallic compound (IMC) layer formed between the pad and thesolder unit, and containing no void at the interface between the copperpad and IMC, and between the IMC and the solder unit.

Through the electrodeposition process without heat treatment,ultra-large copper grains having an average size of at least 10 μm, andcopper films with less impurities, lower electrical resistance, shiningappearance and anti-fingerprint property can be manufactured with lowercosts.

The product of the present invention can be applied to circuit boards,substrates for IC packaging, copper traces and bumps of semiconductorchips, and decorative electroplating.

Through the heat treatment at 200° C. for 1000 hours, the connectingstructure of electric elements having less impurity, lower electricalresistance and better reliability can be manufactured without Kirkendallvoid in the intermetallic compound layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show the electrodeposition equipment used in the presentinvention.

FIG. 3 shows the appearance of the copper film of the present invention.

FIG. 4 shows the SEM image (100×) of the copper film of the presentinvention.

FIG. 5 shows the SEM image (500×) of the copper film of the presentinvention.

FIG. 6 shows the SEM image (3000×) of the copper film of the presentinvention.

FIG. 7 shows the FIB images (5000×) of (A) the ultra-large copper grainsof the present invention and (B) traditional nano-twinned crystalcopper.

FIG. 8 shows the FIB image (1400×) of the ultra-large copper grains ofthe present invention.

FIG. 9 shows the size of the ultra-large copper grains of the presentinvention by the linear intercept method.

FIG. 10 shows the TEM images and SAD patterns of the ultra-large coppergrains of the present invention.

FIG. 11 illustrates the connecting structure of electric elementsincluding the ultra-large copper grains of the present invention.

FIG. 12 shows the FIB image of the connecting structure of electricelements including the ultra-large copper grains of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the manufacturing method of ultra-large copper grains,the copper film and connecting structure of electric elements comprisingthe ultra-large copper grains are discussed in detail in conjunctionwith the accompanying figures.

In the present invention, the electrodeposition process formanufacturing the copper film of ultra-large single crystal grains canbe the electroforming process or the electroplating process.

FIGS. 1 and 2 shows an electrodeposition equipment used in the presentinvention, which includes a cathode 1, an anode 2, an electrolyticsolution 4, a mixer 5, a temperature controller 6 and a power unit 7.The anode 2 and the cathode 1 respectively connect to the power unit 7and are immersed in the electrolytic solution 4.

The temperature controller 6 contacts with the electrolytic solution 4which is fast agitated with the mixer 5. The mixer 5 is a jet mixerlocated between the cathode 1 and the anode 2. The cathode 1 can be arotary cylinder complimentary to the anode 2, as shown in FIG. 1.Alternatively, the cathode 1 and the anode 2 can be plate-shaped, asshown in FIG. 2. The anode 2 can be soluble or insoluble, and made byplatinum, iridium dioxide/titanium, iridium dioxide/tantalumpentoxide/titanium, copper, or copper-phosphorus alloy. The cathode 1can be made by any conductive material such as metal and conductivecarbon. The cathode 1 and the anode 2 are separated by a distance of1-12 cm. The product is deposited on the surface of the cathode 1. Theequipment in FIG. 1 is usually defined as an electroformer since theproduct 3 on the cylindric cathode 1 is collected by a delivery bandover the roller 8. The equipment in FIG. 2 can be defined as anelectroplating if the product 3 remains on the plate cathode 2, or anelectroformer if the product 3 is separated from the cathode 2.

The electrolytic solution is obtained by mixing and dissolving chlorideions, wetting agent, sulfuric acid, copper sulfate pentahydrate(CuSO₄.5H₂O) and sulfur-containing compound having the formula (1)together in deionized water,

R₁—S—C_(n)H_(2n)—R₂   (1)

wherein R₁═—H, —S—C_(n)H_(2n)—R₂, or —C_(n)H_(2n)—R₂;

-   -   R₂═SO₃ ⁻, PO₄ ⁻, or COO⁻;    -   n=2-10.

The electrolytic solution is controlled at 25-55° C. The copper sulfatepentahydrate in the electrolytic solution has a concentration of 125-320g/L. The low concentration of copper sulfate pentahydrate (125 g/L) isoperated at low temperature (25 degree), vice versa. The sulfuric acidin the electrolytic solution has a concentration of 17.6-176 g/L. Thechloride ions are supplied by sodium chloride or hydrochloric acid andhave a concentration of 30-60 ppm in the electrolytic solution. Thewetting agent is polyethylene glycol (PEG) with a molecular weight of200-2000, and has a concentration of 10-200 ppm in the electrolyticsolution. The sulfur-containing compound is alkanesulfonate sulfide(R—S—C_(n)H_(2n)—SO₃ ⁻) and has a concentration of 0.1-5 ppm in theelectrolytic solution. The alkanesulfonate sulfide includes but is notlimited to 3-Mercaptopropanesulfonate (MPS),Bis-(3-sulfopropyl)-disulfide (SPS),3-(2-Benz-thiazolylthio)-1-propanesulfonate (ZPS),3-(N,N-Dimethyl-thiocarbamoyl)- thiopropanesulfonate (DPS), (O-Ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (OPX),3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and3,3-Thiobis-(1-propanesulfonate (TBPS).

In a preferred embodiment, the DC power source with an output 100 A/10Vis used for the power unit 7.

The current density of the current provided by the power unit 7 is 1-80A/dm², and the current efficiency is 94%.

By means of electrodeposition, ultra-large copper grains (ULG) having anaverage size of at least 10 μm are deposited on the cathode. Thethickness is determined according to Faraday's law (δ=0.003445×j×t;wherein δ is thickness (μm), j is current density (A/dm²), and t is timefor electrodeposition (second)). In a preferred embodiment, the depositof ultra-large copper grains each have a size of 18 cm×21 cm×30 μm(thickness).

FIG. 3 shows the ultra-large copper grains of the present invention,which has a rough surface and shining appearance caused by reflection ofthe single crystals. The surface roughness is determined by a surfacemeasuring machine (SURFCOM 130 A of ZEISS). The ten point height ofirregularities (Rz) is 29.40±8.40 μm, and the arithmetical meandeviation (Ra) is 4.67±6.14 μm. The high roughness can reduce the areacontacting with fingers, so that almost no finger-print remains.

FIG. 4 shows the SEM image (100×) of the ultra-large copper grains,which indicates deep indents distributed over the surface.

FIGS. 5 and 6 show the SEM images (500× and 3000×, respectively) of theultra-large copper grains, which indicate the copper crystals with sharpedges.

FIG. 7 compares the FIB (focused ions beam) images (5000×) of theultra-large copper grains of the present invention (A) and thetraditional twinned copper crystals (B). Obviously, the copper grains ofthe present invention have a size about 10-50 times of the traditionaltwinned copper.

FIG. 8 shows the FIB image (1400×) of the ultra-large copper grains ofthe present invention, which indicates that the microstructure isconsistent within a profile of 100 μm.

In FIG. 9, the linear intercept method is used to determine the averagesize of the ultra-large copper grains and the mean grain intercept ismeasured as 10 μm.

FIG. 10 shows the TEM (transmission electron microscope) images and theSAD (selected area diffusion) patterns of the ultra-large copper grains,which verify that each of the ultra-large grains is a single crystal.

In the present invention, the ultra-large copper grains having anaverage size of at least 10 μm, less impurities and lower electricalresistance can be manufactured through the electrodeposition(electroforming or electroplating) process without any heat treatment.

FIG. 11 illustrates the connecting structure of electric elementsincluding the ultra-large copper grains of the present invention. Theconnecting structure of electric elements primarily includes a firstdielectric layer 11, a second dielectric layer 12, copper pads (orcopper traces) 13, 14 and a solder unit 15. The copper pads 13, 14 arerespectively formed on the opposite surfaces of the first dielectriclayer 11 and the second dielectric layer 12. The copper pads 13, 14 aremade by the electrodeposition process aforementioned and thus includethe ultra-large copper grains having an average size of at least 10 μm.The solder unit 15 is formed between the copper pads 13, 14, and can bemade by pure tin, tin/silver/copper alloy, tin/silver alloy or othersolder materials. The intermetallic compound (IMC) layers 16 (Cu₃Sn), 17(Cu₆Sn₅) existing between the copper pads 13, 14 and the solder unit 15are formed by metal diffusion and shifting.

FIG. 12 shows the FIB images of the connecting structures of electricelements including the ultra-large copper grains after heated at 200° C.for 72 hours (A) and 1000 hours (B), and then cut with ion beams. Asshown in FIG. 12, there is no void at the interface between the copperpad 13 and IMC 16, and between the IMC 17 and the solder unit 15 afterhigh heat treatment. In addition, the intermetallic compound layers 16,17 between the copper pad 13 and the solder unit 15 are solid withoutKirkendall void. It is known that the Kirkendall void is adverse toelectron transport and thus reduce conductivity. The connectingstructure of electric elements of the present invention contains noKirkendall void, and the ultra-large copper grains contain very fewimpurities and have low resistance. Therefore, the present invention canprovide a connecting structure of electric elements with superiorreliability.

We claim:
 1. A manufacturing method of ultra-large copper grain withoutheat treatment, comprising: A. providing an electrodeposit equipmentwhich comprises an anode, a cathode, an electrolytic solution, a powerunit, a temperature controller and a mixer; wherein the anode and thecathode respectively connect to the power unit and are immersed in theelectrolytic solution; the temperature controller contacts with theelectrolytic solution to control the electrolytic solution at 25-55° C.;the mixer agitates the electrolytic solution; and the electrolyticsolution is obtained by mixing and dissolving chloride ions, wettingagent, sulfuric acid, copper sulfate and sulfur-containing compoundhaving the formula (1) together in deionized water,R₁—S—C_(n)H_(2n)—R₂ wherein R₁═—H, —S—C_(n)H_(2n)—R₂ or —C_(n)H_(2n)—R₂;R₂═SO₃ ⁻, PO₄ ⁻ or COO⁻; n=2-10; B. performing an electrodepositionprocess using the electrodeposit equipment with a current density of1-80 A/dm² to deposit ultra-large single crystal copper grains having anaverage size of at least 10 μm to form a layer of copper grains on asurface of the cathode.
 2. The method of claim 1, wherein thesulfur-containing compound is alkanesulfonate sulfide(R—S—C_(n)H_(2n)—SO₃ ⁻).
 3. The method of claim 1, wherein thesulfur-containing compound is selected from the group consisting of3-Mercaptopropanesulfonate (MPS), Bis-(3-sulfopropyl)-disulfide (SPS),3-(2-Benzthiazolylthio)-1-propanesulfonate (ZPS),3-(N,N-Dimethylthiocarbamoyl)-thiopropanesulfonate (DPS),(O-Ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (OPX),3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and3,3-Thiobis(1-propanesulfonate (TBPS).
 4. The method of claim 1, whereinthe sulfur-containing compound has a concentration of 0.1-5 ppm in theelectrolytic solution.
 5. The method of claim 4, wherein the coppersulfate in the electrolytic solution has a concentration of 125-320 g/L.6. The method of claim 5, wherein the sulfuric acid has a concentrationof 17.6-176 g/L in the electrolytic solution.
 7. The method of claim 6,wherein the chloride ions have a concentration of 30-60 ppm in theelectrolytic solution.
 8. The method of claim 7, wherein the wettingagent is polyethylene glycol (PEG) having a molecular weight of 200-2000and a concentration of 10-200 ppm in the electrolytic solution.
 9. Themethod of claim 1, wherein the anode and the cathode are separated fromeach other by a distance of 1-12 cm.
 10. The method of claim 1, whereinthe mixer is a jet mixer having a flow rate of 9-45 cm/s.
 11. A copperfilm manufactured by the method of claim 1, comprising a plurality ofthe ultra-large single crystal copper grains having an average size ofat least 10 μm.
 12. An electrolytic solution employed in a manufacturingmethod of ultra-large copper grains without heat treatment, comprising:chemical components including chloride ions, a wetting agent, sulfuricacid, copper sulfate and a sulfur-containing compound having the formula(1),R₁—S—C_(n)H_(2n)—R₂   (1), wherein R₁═—H, —S—C_(n)H_(2n)—R₂ or—C_(n)H_(2n)—R₂; R₂═SO₃ ⁻, PO₄ ⁻ or COO⁻; n=2-10; and deionized waterfor mixing and dissolving the chemical components therein; wherein themanufacturing method performs an electrodeposition process in theelectrolytic solution to deposit ultra-large single crystal coppergrains having an average size of at least 10 μm to form a layer ofcopper grains on a work electrode.
 13. The electrolytic solution ofclaim 12, wherein the sulfur-containing compound is alkanesulfonatesulfide (R—S—C_(n)—H_(2n)—SO₃ ⁻).
 14. The electrolytic solution of claim12, wherein the sulfur-containing compound is selected from the groupconsisting of 3-Mercaptopropanesulfonate (MPS),Bis-(3-sulfopropyl)-disulfide (SPS),3-(2-Benzthiazolylthio)-1-propanesulfonate (ZPS),3-(N,N-Dimethylthiocarbamoyl)-thiopropanesulfonate (DPS),(O-Ethyldithiocarbonato)-S-(3-sulfopropyl)-ester (OPX),3-[(Amino-iminomethyl)thio]-1-propanesulfonate (UPS) and3,3-Thiobis(1-propanesulfonate (TBPS).
 15. The electrolytic solution ofclaim 12, wherein the sulfur-containing compound has a concentration of0.1-5 ppm in the electrolytic solution.
 16. The electrolytic solution ofclaim 15, wherein the copper sulfate in the electrolytic solution has aconcentration of 125-320 g/L.
 17. The electrolytic solution of claim 16,wherein the sulfuric acid has a concentration of 17.6-176 g/L in theelectrolytic solution.
 18. The electrolytic solution of claim 16,wherein the chloride ions has a concentration of 30-60 ppm in theelectrolytic solution.
 19. The electrolytic solution of claim 18,wherein the wetting agent is polyethylene glycol (PEG) having amolecular weight of 200-2000 and a concentration of 10-200 ppm in theelectrolytic solution.
 20. A connecting structure of electric elementsincluding the ultra-large copper grains manufactured by themanufacturing method of claim 1, comprising: a copper pad including theultra-large copper grains having an average size of at least 10 μm; asolder unit on a surface of the pad; and an intermetallic compound (IMC)layer formed between the copper pad and the solder unit, wherein no voidis present at the interface between the copper pad and the IMC, andbetween the IMC and the solder unit.